Blood is regulated by two mechanisms: coagulation and fibrinolysis. The former is a mechanism for forming a thrombus and the latter is a mechanism for dissolving the thrombus. A fibrin is a major component constituting a thrombus and digests into several fibrin degradation products (FDP) through fibrinolysis. The formation and dissolution of fibrin substantially occur at the same times, and D-dimer is an important marker among the FDP produced in fibrin dissolution process. D-dimer is a final degradation product produced when an insoluble fibrin, in which gamma chains are cross-linked to each other by a factor XIII, is degraded by plasmin. It was known that FDP and D-dimer are detected at a higher concentration in plasma of patients suffering from various diseases such as pulmonary embolism, deep vein thrombosis, tumor surgery, disseminated intravascular coagulation, myocardial infarction, trauma, cancer, kidney and liver function impairment than in healthy humans. In particular, FDP and D-dimer have been the most used markers for diagnosing pulmonary embolism and deep vein thrombosis. Because pulmonary embolism and deep vein thrombosis do not have any distinct symptoms showing that the patients may develop pulmonary embolism and deep vein thrombosis, which eventually may lead to death. Also, only less than 20% of these patients were presented as a real positive through the medical examinations such as pulmonary angiography or venous ultrasonography which is widely practiced method for diagnosing these diseases until now. After introducing D-dimer as a diagnostic marker, up to 40% of the patients who are suspected of having thrombotic diseases can be easily diagnosed as a real patient without undergoing an extensive medical examination. There are many diagnostic agents for detecting a D-dimer such as SimpliRED kit (AGEN), an Asserchrom D-Di kit and an STA-Liatesr D-Di kit using an automation system (Diagnostica Stago), a VIDAS kit (BioMerieux SA, France), etc., but most of the diagnostic agents have common problems of low specificity. Also, test results are significantly different among the diagnosis agents since the different monoclonal antibodies; which adopted in each of the said diagnosis agents recognize different cross-linked fibrin degradation products, for instance, preferential binding of low molecular weight fibrin degradation product or of high molecular fibrin products. Actually, D-dimer level in patient's plasma is affected by various factors such as inflammatory diseases, age of patients, pregnancy, administration of an anti-coagulant, etc. in addition to the thrombosis. In particular, an erroneous diagnosis may be made in some test kits using a diagnostic agent specific to low-molecular weight fibrin degradation products since fibrin derivatives in plasma are present as a partially degraded form of cross-linked fibrin rather than a fully digested D-dimer form, especially in the case of the patients suffering from disseminated intravascular coagulation (DIC) syndrome for a long time and being subject to an anti-coagulation treatment (see Abraham Konberg, Blood 1992, vol 80, No 3, 709-717).